There are a variety of manufactured objects where it is desirable to have different functional characteristics on the surface of the part rather than in the body of the object. For example, a power tool handle may require a substantially rigid body, yet a gripping surface that provides cushioning and/or vibration isolation to the operator.
Such characteristics are traditionally imparted by adhesively attaching two different materials to one another (see, e.g., U.S. Pat. No. 6,974,626) or overmolding a soft material onto another, harder, substrate material (see, e.g., U.S. Pat. No. 7,808,816). Disadvantages of overmolding, however, are that it is a complex process that requires expensive tooling, the expensive tooling makes it difficult to customize, and the resulting products may encounter adhesion problems during extended field use.
Additive manufacturing with different grades of materials offers some promise for these types of applications, but changing materials during additive manufacturing can slow the process, mechanical properties can be limited by the materials available, and again adhesion issues between different materials may be encountered during extended field use.
Accordingly, there is a need for new ways to manufacture three-dimensional objects as a single, unitary, piece of material, which objects have surface regions with functional characteristics that differ from other portions of the object.